1. Technical Field
Embodiments relate to a rechargeable battery and associated methods.
2. Description of the Related Art
A cathode-active material of a lithium rechargeable battery is one of four major components necessary for fabrication of a rechargeable battery. It is an important factor that accounts for 40% of material costs, and determines the battery capacity. Even though a lithium cobalt oxide (LCO), e.g., LiCoO2, compound has been widely used as a cathode-active material, use of a ternary cathode-active material is gradually increasing due to a rapid rise in the price of cobalt, and an increased demand for high-capacity batteries. In the case of LCO-based cathode-active materials, cobalt is responsible for about 60% of the total production cost. However, the ternary cathode-active material accounts for only about 15 to 17% of the battery production cost, which is thus capable of saving about 20% of the production cost based on the whole battery.
However, such a ternary cathode-active material, e.g., nickel cobalt manganese (NCM), e.g., Li[NiMnCo]O2, or nickel cobalt aluminum (NCA), e.g., Li[NiAlCo]O2, has not been widely used due to various problems including, e.g., dissolution of Ni or Mn ions into an electrolyte, reduction of the dissolved metal ions at the anode surface leading to metal dendrite growth causing metal dendrite penetration of a separator, and consequently occurrence of an internal short circuit thus resulting in a voltage drop. That is, in a cylindrical battery typically used in notebook computers, a charged battery may be exposed to a high temperature of about 40° C to about 60° C. due to heat generation from a main body of the notebook computer. In a battery using the ternary cathode-active material, metal cations dissolved from the cathode-active material, e.g., nickel or manganese ions, may undergo reduction by receiving electrons from a surface of the anode-active material, which may result in undesirable dendritic growth of nickel or manganese metal. Then, the grown dendrite may penetrate into a thin (˜10 to 20 μm) polyolefin separator film, which in turn may lead to problems associated with the occurrence of a micro short circuit inside the battery, and a poor voltage accompanied by a voltage drop of the charged battery.
Further, the ternary active material may suffer from a low discharge voltage when compared to LCO-based active materials. Therefore, in order to fabricate a battery for, e.g., notebook computers, etc., the active material should satisfy a driving electric power equivalent to that of LCO, so it may be necessary to compensate for a low voltage relative to LCO by increasing a capacity of the battery using the ternary active material (hereinafter, referred to as “ternary battery”). To this end, it may be desirable to greatly increase initial capacity of a ternary battery relative to a battery using the LCO-based active material (hereinafter, referred to as “LCO-based battery”). It may also be desirable to solve the problems associated with a short battery life and a drop of the voltage upon exposure of the battery to high temperatures for a long period of time.